1. FIELD OF THE INVENTION
In one of its aspects, the present invention relates to a sulfur determination electrode. In another of its aspects, the present invention relates to the use of such an electrode in the electrolytic detection of sulfur in a sample containing oxidizable sulfur. In yet another of its aspects, the present invention relates to a process for manufacturing a sulfur detection electrode.
2. DESCRIPTION OF THE PRIOR ART
As concern for our environment grows, the governmental agencies of many countries are imposing restrictions and regulations concerning the disposal of chemicals and contaminants into the environment. With the passage of time these restrictions and regulations are becoming much more rigid in terms of the quantity of chemicals and contaminants which may be released into the environment. In part, this is due to discoveries relating to the extent to which these chemicals and contaminants affect the environment. Accordingly, the ability to detect and monitor these chemicals and contaminants is becoming increasingly necessary in order to control release thereof in a manner which complies with the governmental restrictions and regulations.
Sulfur-containing compounds are one group of compounds which have been found to be particularly detrimental to the environment. Typically, such compounds comprise and/or release oxidizable sulfur such as sulfide ion (e.g. HS.sup.-, S.sup.2- and the like) and mercaptans (RSH). Thus, when these sulfur-containing compounds are released into the environment, sulfur is also released directly or indirectly. Sulfur-containing compounds are commonly found in the waste water effluent from pulp and paper plants, as well as from oil and gas refineries.
Heretofore, various methods have been employed to detect the presence and concentration of sulfur such as sulfide ion in aqueous samples.
One method involves the use of wet titration for measurement of the sulfide ion concentration. Once this concentration is determined, the concentration of the actual sulfur-containing compound may be determined. Unfortunately, the wet titration method is neither rapid nor efficient to serve the purposes of industry which require the ability to make multiple on-line measurements in a rapid fashion.
Another method for measurement of sulfide ion concentration involves utilizing ion chromatography coupled with electrochemical detection. See, for example, Anal. Chem., 54(3), 582-5 (Bond et al). The requirement of utilizing two analytical techniques renders this method cumbersome and, in some cases, lacking in precision and accuracy.
Yet another method for measurement of sulfide ion concentration involves utilizing a potentiometric method. See, for example, any one of Anal. Chem., 40(7), 1055 (1968) [Hseu et al], Anal. Chim. Acta, 51, 231 (1970) [Mascini et al] and Anal. Lttrs., 1(13), 825 (1968) [Light et al].
Yet another method for measurement of sulfide ion concentration utilizes a sulfide ion-selective membrane electrode obtained by incorporating silver sulfide into a silver silicon rubber matrix. See, for example, Anal. Chem., 39 (13) 28A (1967) [Pungor]. This method makes use of a sulfide-based ion-selective electrode (also known as an Orion electrode) to determine sulfide ion concentration in an aqueous solution. The detection of sulfide using this method is indirect for most applications insofar as the sulfide must be initially reacted with silver or lead to form silver or lead sulfide, each demonstrating low solubility. Thus, excess sulfide ion remaining in solution may then be detected and measured using the Orion electrode. In some cases, the Orion electrode may be used to make direct measurements of sulfide if the pH of the aqueous sample is buffered (or otherwise adjusted) to a value of 12. Thus, the method is relatively cumbersome and inefficient since in the indirect mode additional cost (for silver and lead chemicals), time and potential experimental error are incurred over and above the underlying electrochemical technique. Further, in the direct mode, additional cost (buffering agent) and time are incurred over and above the underlying electrochemical technique. Moreover, the Orion electrode is sensitive to a range of contaminants that may also be present in the aqueous sample and thus, it is important to know, at least qualitatively, the composition of the aqueous sample.
A Cu-O-loaded element for hydrogen sulfide (H.sub.2 S) detection has recently been reported in Chem. Lttrs., 575 (1991) [Maekawa et al]. However, there is no indication that this method is useful in the determination of the concentration (i.e. quantitative determination) of sulfide ion in an aqueous solution.
In light of the foregoing, there still exists a need for an electrode which allows for rapid, precise and accurate determination of sulfur from samples containing oxidizable sulfur, such as (i) aqueous samples comprising sulfide ion, and (ii) other sulphur containing compounds such as mercaptans.